The EPA and CARB regulate internal combustion engine emissions. Initially, the majority of these regulations were focused on stack emissions. But increasingly stringent environmental regulations and a heightened consciousness of environmental conservation have also mandated cleaner operation of hydrocarbon powered sources such as automobiles, boats, trucks, motorcycles and the like. It is anticipated that new federal and CARB emissions regulations will require these discharged gases to be cleaned and will include crankcase gases as part of the regulated diesel engine emissions.
Combustion gas is blown out from an engine combustion chamber into a crankcase through a clearance between a piston and a cylinder resulting in blow-by gas. During the operation of the engine, small amounts of hot combustion gases leak past the piston rings and through the oil circulating within the crankcase to create a pressurized mixture of air, exhaust gases and atomized oil. At small throttle openings or low loads, for diesel engines, the amount of blow-by gas is not troublesome but at large throttle openings the amount of blow-by gas is such that considerable pressures can develop in the crankcase. If left unvented, this pressure may lead to the penetration of oil seals between the crankshaft and the engine block resulting in an undesirable loss of engine oil and pollution in the form of constant oil leakage from the vehicle. Sufficient venting of such gas is, therefore, required. In some internal combustion engines, baffles are provided in front of the vent openings for removing some of the oil in the blow-by gases. The remaining harmful emissions are vented into the air via a road draft tube or, through a PCV valve, are returned to the induction line of the internal combustion engine upstream of the air filter or passed into an air-oil separator. While venting through a road draft tube reduces the pressure in the crankcase, oil is still allowed to escape from the engine into the outside environment.
As a result, blow-by devices such as pollution control valves have become required standard equipment for all automobiles. These blow-by devices capture emissions from the crankcase of a hydrocarbon burning engine and, in a closed system, communicate them to the air intake device for combustion. The emissions generated from the crankcase of diesel engines are heavily laden with oil and contain other heavy hydrocarbons. Accordingly, air-oil separators have been developed in an effort to make the operation of such engines cleaner and more efficient. An air-oil separator contains a filter and may be either integrated in the valve cover or inserted as an individual component. The density of the filter used is determined by the pressure difference between the crankcase and the compressor inlet or the atmosphere for an open system. A partial vacuum is created at the compressor inlet. The greater the available partial vacuum, the denser the filter may be and the "cleaner" the emission gas. The air-oil separators filter out a large proportion of the oil contained in the blow-by gas before the gas passes into the open or is returned to the engine. Such devices also function to filter air in an air inlet flow line to an engine, separate oil and other hydrocarbons emitted from a contaminated engine atmosphere, and regulate the pressure within the engine crankcase.
When the air-oil separators presently available on the market are used, a considerable quantity of oil still breaks through. None of these separators, therefore, has provided an entirely satisfactory solution to the aforementioned problems. U.S. Pat. Nos. 5,140,957 to Walker and 5,479,907 to Walker, Jr. disclose crankcase ventilation systems which use the differential pressure between the crankcase and the turbocharger inlet to force air through a separation device. These systems, however, use conventional automotive filters such as polyester fiber filters which are not 100 percent effective. The systems also fail to disclose a bypass and control valve to handle the different pressure levels in the crankcase. A crankcase ventilation system with a bypass valve and a control valve is shown in U.S. Pat. No. 4,329,966 to Ramsley. However, the bypass is only operated when the vacuum increases beyond a predetermined level.
The air filters used in the air-oil separators of the prior art are generally composed of wire mesh, steel wool or foam. These filters are generally less than 70 percent effective and are driven by pressure in the crankcase. Traditionally, the air-oil separator device is connected by a flow line to the inlet duct of the turbocharger.
The increasing governmental regulation and environmental awareness requires careful treatment of emissions from hydrocarbon burning engines. A need exists, therefore, to provide an improved apparatus for separating contaminants from the crankcase emissions of hydrocarbon powered engines in an efficient manner, minimizing the extent of contaminants released into the environment and improving the operation of the engine. This invention uses the reduced pressure generated within the turbocharger itself to drive a high efficiency filter or separation device. The cleaned gas can then pass through the compressor and aftercooler without fouling the flow passages.